1. Field of Invention
The invention relates to a method for patterning a thin film on a substrate, and more particularly to a method for reducing resist sensitivity.
2. Description of Related Art
In material processing methodologies, pattern etching comprises the application of a layer of radiation-sensitive material, such as photo-resist, to an upper surface of a substrate, the formation of a pattern in the layer of radiation-sensitive material using photo-lithography, and the transfer of the pattern formed in the layer of radiation-sensitive material to an underlying thin film on the substrate using an etching process. The patterning of the radiation-sensitive material generally involves exposure of the radiation-sensitive material to a pattern of electromagnetic (EM) radiation using, for example, a photo-lithography system, followed by the removal of the irradiated regions of the radiation-sensitive material (as in the case of positive tone resist), or non-irradiated regions (as in the case of negative tone resist) using a developing solution.
As the critical dimension (CD) decreases, there is a need to increase the resolution of the pattern of EM radiation (Resolution) and the sensitivity of the resist (Sensitivity) while keeping the line width roughness (LWR) of the resulting pattern within acceptable limits. It is known in the art that there is a tradeoff relationship between Resolution, LWR, and Sensitivity, often called the LRS tradeoff triangle. Conventional techniques which seek to improve one of the three parameters often improve at the unacceptable expense of one or both of the other parameters. Extreme ultra violet (EUV) lithography shows promising results for feature sizes below 40 nm. However, EUV resist sensitivity is one of the challenges for EUV lithography. As noted in the LRS tradeoff above, it is very difficult to obtain simultaneous improvements in resolution, LWR, and sensitivity. There is need for a method and system that allows the reduction of resist sensitivity significantly without impact to the LWR and resolution in order to achieve an enabling throughput for EUV lithography.